Service providers around the world have already begun lab testing and trial deployments of G.fast technology. The majority of this early work has been accomplished with close partnerships with potential suppliers, usually working with a single chipset vendor. That is, the customer modem and service provider distribution point unit are both built using G.fast chips from that single vendor. This approach has the advantage of enabling rapid prototypes and trials, but is less suited for longer term, larger scale deployments.

Now, one of the key operator requirements for the technology is interoperability between chipsets. Operators see interoperability as a market driver in enabling choice within their supply chain, both for their initial deployments and future network upgrades. To this end, vendors have been working to enable interoperability between chipsets, while still supporting the full feature sets and capabilities of the technology.

About G.fast
G.fast (ITU-T Specification G.9701) is a physical layer communication protocol, allowing two devices to transmit bi-directional data at bit rates around 1 Gbit/s over a single copper pair. Put simply, it's a high-speed connection on a telephone wire (very low grade copper wire) to enable broadband delivery into a subscriber's home or business.

The technology is intended to expand fiber-like data rates into places where fiber presents a challenge to deploy. Fiber connectivity can provide speeds upwards of 10 Gbit/s, but at the cost of bringing the fiber, a new "cable" in many installations, to the subscriber's terminal.

This can present a challenge based on a number of potential issues: cost of the install (fiber pretty much always requires a truck roll), access to wiring spaces (installing new fiber in an existing apartment building might be impossible), safety (most regulators require fiber interface access be "protected" from the consumer), etc.

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When deployed in conjunction with fiber, G.fast provides service providers with a convenient technology to connect with subscriber equipment inside the residence or business without installing new cabling or fiber at the customer's premises. Working distances for G.fast is up to 300m, and can provide aggregate data rates upwards of 300 Mbit/s at the 300m mark. This allows the operator to locate the fiber termination equipment in a location convenient for installation and service, such in the telecom room of an apartment or office building, or on a telephone pole located at the end of street.

Readying G.fast for deployment
With almost every new technology, vendors initially develop solutions that work within their own company, may implement only some of the requirements of the standard, and may not be compatible with implementations from other companies. In this way, G.fast development has not been any different from other technologies.

Some of these requirements may not prevent systems from reaching the "showtime" state with other devices, but could impact the performance of the systems while noise or other factors impact the line. This could result in the line retraining more often than when both devices -- customer premises equipment (CPE) and distribution point unit (DPU) -- implement all the requirements/features defined in the ITU-T specifications.

To support the development of interoperable G.fast solutions, the industry has taken two complementary paths with oversight from the Broadband Forum: regular plugfests and the development of a certification program.

The plugfest events have provided opportunities for vendors to cooperate and test solutions in a neutral environment. These events have enabled basic interoperability between some chipsets, as was demonstrated during the Broadband World Forum in October 2016.

Following up the plugfest events is the development of a certification program, aimed at testing both the interoperability of systems and their implementation of key features of the G.fast specifications.

Features such as fast rate adaption enable the G.fast devices to quickly adjust to large changes of noise on the line, without dropping the link. Similarly, other key features, such as bit swapping, seamless rate adaptation, and retransmission also contribute to the stability of the G.fast link (keeping subscribers online and happy). The certification test plan defines detailed procedures to thoroughly test these requirements, according to the G.fast specification, i.e., standards compliance.

The overall program will require certified devices be tested (and achieve passing results) against other previously certified devices, ensuring the certified devices are both interoperable and compliant to the specifications. The program is also designed to "refresh" the list of required test partners, to prevent the testing to become "stale" or out of date with currently deployed devices.

Service providers are able to leverage the program and certified devices to ensure their networks are built using equipment that will be interoperable. Certified devices will have been tested against other G.fast devices, including other chipsets. The certification testing verifies these critical G.fast features used to provide network stability, ensuring certified devices implement features designed to improve the stability and performance of the G.fast line when deployed to customers.

— Lincoln LaVoie, Senior Engineer, Broadband Technologies, UNH-IOL

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